1. Field of the Invention
The present invention relates to an exposure apparatus and exposure method used when producing a semiconductor integrated circuit, a liquid crystal display, a pickup device, a thin film magnetic head, or another device, more particularly relates to an exposure apparatus and exposure method for exposing an image of a pattern formed on a mask on to a substrate while making the mask and substrate engage in a synchronous scan motion.
2. Description of the Related Art
In the production of a semiconductor circuit, liquid crystal display, pickup element, thin film magnetic head, or other device, the image of a fine pattern formed on a photomask or reticle (hereinafter referred to as a xe2x80x9cmaskxe2x80x9d when spoken of in general) is repeatedly transferred using an exposure apparatus through a projection optical system to a semiconductor wafer or glass plate etc. coated with a photoresist or other photosensitive agent.
In the production of a semiconductor circuit, use is made of a step-and-repeat type reduction projection exposure apparatus (so-called xe2x80x9cstepperxe2x80x9d) which places the substrate on a substrate stage able to freely move in two dimensions, repeatedly makes the substrate move in steps by this substrate stage, and successively exposes and transfers the image of the pattern of the reticle on to shot areas of the substrate.
In recent years, along with the increasingly large size of substrates and increasing fineness of patterns, a step-and-scan type exposure apparatus which transfers the image of a pattern formed on a reticle to a substrate while making the substrate stage carrying the substrate and a reticle stage carrying the reticle formed with the pattern to be exposed move synchronously has come into use.
Even with exposure using the step-and-scan type exposure apparatus, like with the stepper, the photoresist or other photosensitive agent is repeatedly coated on a substrate already formed with a pattern so as to expose different patterns. Therefore, it is necessary to measure the relative position of the substrate and the pattern formed on the reticle to be projected with a high accuracy and to precisely match the relative positions of the substrate and reticle at the time of exposure. In particular, in the step-and-scan type exposure apparatus, it is necessary to accurately control the relative positions and scan speeds of the reticle and substrate at the time of start of exposure.
In the production of the device, however, in order to reduce the manufacturing costs etc., it is required to increase the number of substrates which can be processed by the exposure apparatus in a unit time (throughput). The above step-and-scan type exposure apparatus performs exposure while making the reticle and substrate engage in synchronous scan motion, but to improve the throughput, it is necessary to increase the scan speeds of the reticle stage and substrate stage at the time of exposure.
The step-and-scan type exposure apparatus moves the reticle stage and substrate stage by a constant speed at the time of exposure, so at the time of start of the scan, it is necessary to make the reticle stage and substrate stage accelerate from the stationary state to the constant scan speed, while at the time of end of the scan, it is necessary to decelerate the reticle stage and substrate stage moving at the constant scan speed to make them stop. Improvement of the throughput requires the scan speed of the reticle stage and substrate stage to be raised, but if the scan speed is raised, the acceleration at the time of acceleration or deceleration of the reticle stage also has to be made higher. Further, after the end of scan exposure of one shot area on the substrate and before the scan exposure of the next shot area, movement of the substrate is controlled so as to start the movement of the substrate in the nonscan direction perpendicular to the scan direction before the speed component relating to the scan direction in which the substrate is moved at the time of scan exposure becomes zero (stepping action) and to start the acceleration of the substrate in the scan direction before the stepping action is completed, that is, before the speed component of the substrate relating to the nonscan direction becomes zero. Therefore, the time of movement of the substrate between shot areas is shortened, so shortening of the acceleration and deceleration periods of the reticle stage, that is, an increase of the acceleration, has been requested.
If a stage moves, the position at which the substrate or reticle etc. is carried may shift. To prevent this, in the step-and-scan type exposure apparatus, the reticle is held by suction on the reticle stage, while the substrate is held by suction on the substrate stage. Therefore, even if a certain degree of force is applied to the reticle or substrate in the scan direction or the opposite direction due to acceleration or deceleration, the position of the reticle on the reticle stage and the position of the substrate on the substrate stage will not shift.
If the acceleration is increased at the time of acceleration or deceleration of the reticle stage or substrate stage, however, the position of the reticle or substrate may shift even if held by suction. The substrate is held by suction on the substrate stage over substantially the entire bottom surface, so the suction force can be made relatively high, but the reticle is a synthetic quartz or other glass plate on one surface of which a pattern is formed and illumination light for exposure passing through the reticle is projected on to the substrate, so it is only possible to hold the periphery of the bottom surface of the reticle (pattern formation surface) on the reticle stage.
Further, when providing a reduction projection type projection optical system with a projection magnification of 1/xcex2 (where xcex2 is for example 4, 5, 6, etc.), it is necessary to set the scan speed of the reticle stage to xcex2-times the scan speed of the substrate stage. Therefore, the acceleration at the time of acceleration or deceleration of the reticle stage has to be set higher by that amount. If the reticle becomes offset, the image of the pattern formed on the reticle will be transferred to the substrate in a state with the relative positions of the reticle and substrate offset, so the device produced is liable to become a defective one which does not give the desired performance. In particular, when producing a device formed with a fine pattern, even a slight offset could lead to a defective product.
Further, in addition to the time of exposure of the substrate, for example, at the time of alignment or exchange of reticles or moving a reticle from the alignment position to an exposure position (position of start of acceleration), if the acceleration of the reticle stage is high, there is the problem that offset of the reticle will occur in the same way as above and the accuracy of alignment with the substrate will fall.
The present invention was made in consideration of this problem in the prior art and has as its object to enable exposure with a high throughput without allowing offset to occur along with movement of the mask. Further, it has as its object to enable exposure to stop being continued in a state of offset in the event that offset occurs along with movement of the mask.
To solve the above problem, according to a first aspect of the present invention, there is provided an exposure apparatus for exposing a substrate through a mask formed with a pattern, the exposure apparatus characterized by being provided with a stage which holds and moves the mask, an acceleration detection device which detects information relating to acceleration of the stage, and a control device which controls movement of the stage so that the acceleration of the stage as based on the information detected by the acceleration detection device becomes within a range of acceleration of the stage found in advance where offset will not occur in the mask.
According to the present invention, since movement of the stage is controlled so that the acceleration of the stage as based on the information detected by the acceleration detection device becomes within a range of acceleration of the stage where offset will not occur in the mask, offset of the mask is not caused at the time of exposure. Further, by making the stage move at a higher acceleration within the range where offset will not occur in the mask, it is possible to perform exposure with a high throughput without allowing offset to be caused along with movement of the mask stage.
To solve the above problem, according to a second aspect of the present invention, there is provided an exposure apparatus for exposing a substrate through a mask formed with a pattern, the exposure apparatus provided with a stage which holds and moves the mask, an acceleration detection device which detects information relating to acceleration of the stage, a posture detection device which detects a posture of the mask on the stage, and a control device which initiates detection by the posture detection device when the acceleration of the stage as based on the information detected by the acceleration detection device becomes out of the range of acceleration of the stage found in advance where offset will not occur in the mask and performs processing for notifying an operator of the fact that it has judged that offset has occurred in the mask when that is the case.
According to the present invention, when the acceleration of the stage as based on the information detected by the acceleration detection device becomes out of the range of acceleration where offset will not occur in the mask, the posture detection device is used to detect the posture of the mask. When offset of the mask is detected by the results of detection of the posture detection device, that fact is notified to the operator. Therefore, the exposure processing is not liable to continue while the offset of the mask remains and a defective product is not liable to be caused.
Further, the range of acceleration where offset of the mask will be caused is not clearly separated from the range of acceleration where offset of the mask will not be caused. For example, there is a range of acceleration where offset of the mask will sometimes occur and sometimes not occur even at the same acceleration depending on the temperature, humidity, and other surrounding conditions. To realize high throughput, requests may conceivably be made not to move the stage in the range where offset will never occur, but to increase the acceleration of the stage even if there is a possibility of movement of the mask. By application of the present invention, it is also possible to respond to such requests. Even if the acceleration is set too high and offset of the mask occurs, it is possible to prevent exposure processing from continuing while the offset remains.
In the exposure apparatus according to the second aspect of the invention, further provision is made of a posture adjustment device which adjusts the relative positional relationship between the mask on the stage and the substrate (for example, the posture of the mask or substrate etc.) and the relative positional relationship of the mask and substrate is made adjustable so as to cancel out offset by the posture adjustment device when the control device judges that offset has occurred in the mask. When judging that offset has occurred in the mask, the control device adjusts the relative positional relationship between the mask and substrate by the posture adjustment device so as to cancel out the offset, so even if offset of the mask occurs, that deviation is automatically corrected. This is desirable in obtaining a high throughput.
In the exposure apparatuses of the first aspect and second aspect of the invention, the range of acceleration can be derived by a process of trial and error by repeatedly detecting offset of the mask while increasing or decreasing the acceleration of the stage in steps.
In the exposure apparatuses of the first aspect and second aspect of the invention, the range of acceleration is derived at least at one of the time of startup of the exposure apparatus and the time of exchange of the mask.
In the exposure apparatuses of the first aspect and second aspect of the invention, it is possible to further provide a storage device which stores the range of acceleration of the stage.
In the exposure apparatuses of the first aspect and second aspect of the invention, it is possible to further provide a sensor which detects information relating to an ability of the stage to hold the mask and to change the range of acceleration by the control device in accordance with the detected information. As the sensor in this case, it is possible to employ a vacuum sensor etc. for measuring the holding capability (vacuum pressure).
To solve the above problem, according to a third aspect of the present invention, there is provided an exposure method for exposing a substrate through a mask formed with a pattern, the exposure method characterized by finding in advance a range of acceleration of a stage holding and moving the mask or the substrate where offset will not be caused in the mask or the substrate due to acceleration or deceleration of the stage and performing exposure while controlling the movement of the stage within the range of acceleration.
According to the present invention, in the same way as the exposure apparatus of the first aspect of the invention, it is possible to perform exposure at a high throughput without allowing offset to occur in the mask or substrate at the time of exposure.
To solve the above problem, according to a fourth aspect of the present invention, there is provided an exposure method for exposing a substrate through a mask formed with a pattern, the exposure method characterized by finding in advance a range of acceleration of a stage holding and moving the mask or the substrate where offset will not be caused in the mask or the substrate due to acceleration or deceleration of the stage, detecting information relating to acceleration of the stage and detecting the presence of offset of the mask or the substrate when the acceleration of the stage as based on the information is outside of the range of acceleration, and adjusting the relative positional relationship between the mask and the substrate (for example, the posture of the mask or substrate etc.) so as to cancel out offset when judging that offset has occurred in the mask or the substrate.
According to the present invention, in the same way as the exposure apparatus of the second aspect of the invention, the relative positional relationship between the mask and substrate is adjusted to as to cancel out offset when judging that offset has occurred in the mask or substrate, so even if offset of the mask or substrate occurs, that deviation is automatically corrected. This is desirable in obtaining a high throughput.
In the exposure method according to the fourth aspect of the invention, when judging that offset has occurred in the mask or substrate, it is possible to perform processing to notify an operator of that fact. Since the posture of the mask or substrate is detected when the acceleration detected by the acceleration detection device is outside of the range of acceleration where offset will not occur in the mask or substrate and the fact that offset of the mask or substrate is detected is notified to the operator when that is the case, there is no danger of exposure processing continuing while the offset of the mask or substrate remains and causing a defective product.
In the exposure methods according to the third aspect and fourth aspect of the invention, it is also possible to detect information relating to the capability of the stage to hold the mask and to change the range of acceleration in accordance with the detected information.
Note that xe2x80x9cwhere offset will not occur in the mask or substratexe2x80x9d includes not only the case where the amount of offset is completely zero, but also the case where it is deemed to be substantially zero, for example, when it is not more than a predetermined amount negligible in precision in the production process of the device.
Further, the upper limit or range of the xe2x80x9cacceleration of the stage where offset will not occurxe2x80x9d differs according to the force of the stage holding the mask or substrate (holding force). For example, in a stage where the holding force fluctuates due to the environment or aging factors etc. or where the holding force is made variable, the upper limit or range of the acceleration also changes. Therefore, the upper limit or range of the acceleration may be set in accordance with the maximum value of the holding force of the stage, but is preferably set in accordance with the actual holding capability. Further, the xe2x80x9cacceleration detection devicexe2x80x9d is not limited to an acceleration meter, vibration sensor, laser interferometer for detecting positional information of the stage, or other device for directly or indirectly measuring the acceleration and includes for example a control system for giving drive instructions to a drive system for driving the stage or other device for storing or generating information relating to acceleration. At this time, it is also possible to detect not the acceleration itself, but the speed or other related information.
The exposure apparatus of a fifth aspect of the present invention is an exposure apparatus for exposing a substrate through a mask formed with a pattern, comprised of a stage which holds and moves the mask, an acceleration detection device which detects information relating to acceleration of the stage, a posture adjustment device which adjusts a relative positional relationship between the mask and the substrate, a storage device in which offset information showing the relationship between the acceleration of the stage and the offset of the mask found in advance is stored, and a control device which retrieves from the storage device the offset information corresponding to the acceleration of the stage based on information detected by the acceleration detection device and adjusting the relative positional relationship of the mask and the substrate (for example, the posture of the mask or substrate) so as to cancel out the offset by the posture adjustment device.
The exposure method of a sixth aspect of the present invention is an exposure method for exposing a substrate through a mask formed with a pattern, the exposure method comprising performing exposure by finding in advance information showing offset occurring in the mask or substrate due to acceleration or deceleration of a stage for holding and moving the mask or the substrate in relation with the acceleration, detecting information relating to acceleration of the stage, and adjusting a relative positional relationship between the mask and the substrate (for example, the posture of the mask or substrate etc.) so as to cancel out the offset based on offset information corresponding to the acceleration of the stage as based on the detected information.
The exposure apparatus of a seventh aspect of the present invention is an exposure apparatus for exposing a substrate through a mask formed with a pattern, comprised of a stage which holds the mask, a detection device which detects information relating to acceleration of the stage, and an adjustment device which adjusts a relative positional relationship between the mask and the substrate (for example, the posture of the mask or substrate etc.) at the time of exposure in accordance with the detected information.
The exposure apparatus of an eighth aspect of the present invention is an exposure apparatus for exposing a substrate through a mask formed with a pattern, comprised of a stage which holds the mask, a detection device which detects information relating to acceleration of the stage, and a control device which performs at least one of an operation for recovery from exposure error occurring due to the offset due to movement of the stage and notification of the exposure error.